1. Field of the Disclosure
The present disclosure relates to a rotation input device.
2. Description of the Related Art
Input devices included in in-vehicle apparatuses, such as a car navigation system, a car audio system, and a car air conditioning system, include rotation input devices each including an operation knob that is rotated about a single shaft. An operator rotates the operation knob, thereby inputting a proper instruction to such an in-vehicle apparatus.
In some rotation input devices, when the operator rotates the operation knob, an electromagnetic brake applies a braking force to the operation knob in accordance with a rotation position of the operation knob, thus allowing the operator to recognize an operation range and operation limits.
For example, Japanese Unexamined Patent Application Publication No. 2005-19113 discloses a tactile force applying input device in which when an operation knob is rotated beyond its operation range, an electromagnetic brake prevents rotation of the operation knob and provides a tactile barrier to the operator.
In this case, when the operator intends to rotate the operation knob in the opposite direction, the electromagnetic brake has to be released. If the operation knob is completely locked, it is difficult to determine a direction in which the operation knob is to be rotated. Disadvantageously, the electromagnetic brake cannot be released. The above-described tactile force applying input device therefore includes an elastic member disposed at the middle of a drive shaft so that the operation knob is rotatable when the electromagnetic brake applies a braking force. Thus, the operator can determine the direction in which the operation knob is to be rotated.
In the above-described tactile force applying input device disclosed in Japanese Unexamined Patent Application Publication No. 2005-19113, while the electromagnetic brake prevents the drive shaft from rotating, if the operation knob is further rotated in the same direction as the direction in which the drive shaft was rotated until the rotation was prevented, the elastic member is elastically deformed, so that the operator can feel a tactile barrier. After that, when the operator rotates the operation knob in the opposite direction, a rotary encoder detects the angle and direction of rotation of the operation knob and the prevention of the drive shaft rotation by the electromagnetic brake is released, so that the operation knob is unlocked.
If the operator, who has felt the tactile barrier, rotates the operation knob in the opposite direction by a small angle, the rotary encoder cannot detect the angle of rotation (hereinafter, referred to as a “rotation angle”) of the operation knob in the opposite direction and the direction of rotation (hereinafter, referred to as a “rotation direction”). Unfortunately, the drive shaft is continuously prevented from rotating by the electromagnetic brake and the locked operation knob is not unlocked.
These and other drawbacks exist